In the art of making lenses, when a lens, such as a spectacle lens, is processed so that the lens may be fitted into a lens frame of a spectacle frame, the peripheral face of an uncut lens is ground by a grinder, or cut by a cutter. In this manner, peripheral portion of the uncut lens is formed into a prescribed shape in accordance with data corresponding to the shape of the lens frame of the spectacle frame.
Prior art examples of the known processing apparatus for this purpose include, as disclosed in Japanese Patent Application Laid-Open No. 2001-18154, apparatuses in which, after the peripheral portion of a lens is processed by the flat grinding or the beveled grinding using a rotating tool (a grinder), which is freely rotated to grind the peripheral portion of a lens. The prior art apparatuses also conduct chamfering and grooving as steps in the finishing of the peripheral portion of the lens by using a grinder for chamfering and a grinder for grooving, which are coaxially disposed.
In Japanese Patent Application Laid-Open No. 2001-87922, an apparatus for chamfering and grooving the peripheral portion of a lens using a single ball end mill is disclosed.
However, as shown in FIG. 15, since conventional apparatuses, such as those described above, are equipped with a grinder for chamfering the concave face of the lens and a grinder for chamfering the convex face of the lens, wherein these grinders are formed integrally with a grinder for grooving that is disposed between these two grinders for chamfering, it occasionally occurs that, as shown in the portion A of FIG. 15, the grinder for grooving protrudes radially beyond the outside of the periphery of both grinders for chamfering, and one of the grinders for chamfering protrudes laterally at a peripheral portion so as to contact the lens-holding shaft and interfere with lens processing. When this problematical arrangement takes place, in particular, such as in the case of a lens having a small diameter, chamfering cannot be properly conducted. In the example of the conventional apparatus of FIG. 15, when changing the chamfering angle, the desired chamfering angle is achieved by inclination of the shaft upon which the grinder for chamfering is mounted. This method for changing the chamfering angle is problematical in that, in order to conduct chamfering while the shaft is inclined at various desired angles, the apparatus required includes complicated driving mechanisms and supporting mechanisms for the tool, and the size of the apparatus increases.
In the example described in FIG. 15, the grooving is conducted by using the tip of a ball end mill and the chamfering is conducted by using a side face of the same single ball end mill. Since the outer diameter of the ball end mill is determined by the width of the groove formed at the outer peripheral face of the lens, it becomes necessary to perform a plurality of processing steps, each step is conducted at a different position on the face of the lens, or the processing must be conducted while the tool is moved when the chamfering area is great (or the curvature of chamfering is great). Therefore, problems arise in that the processing time increases and the control operation for the apparatus becomes complex and difficult.
The present invention has been made to overcome the above problems with the prior art lens processing apparatuses. One object of the present invention is to provide an apparatus for processing a lens that can achieve chamfering and grooving of a lens, in particular a lens having a small diameter, by using a simple mechanism that can achieve a desired chamfering in a short time.